(SEM III) THEORY EXAMINATION 2025-26 PHYSICAL PHARMACEUTICS I

SECTION A – Short Answer Section

This section contains brief conceptual questions related to physical pharmacy such as solubility, viscosity, micelles, and surface phenomena. These questions test the basic understanding of pharmaceutical physical chemistry and its applications in drug formulation.

Question 1: What is Solubility Parameter?

Answer:
The solubility parameter is a numerical value that indicates the solubility characteristics of a substance. It helps predict whether two substances will dissolve in each other.

Significance:

Used to select suitable solvents for drugs.

Helps in predicting drug–polymer compatibility in pharmaceutical formulations.

Question 2: Define Critical Micellar Concentration (CMC).

Answer:
Critical Micellar Concentration (CMC) is the minimum concentration of surfactant in a solution at which micelles start to form.

Below CMC → surfactants exist as individual molecules.
Above CMC → surfactants form micelles.

Factors affecting CMC:

Temperature

Nature of surfactant

Presence of electrolytes

Question 3: Define Viscosity.

Answer:
Viscosity is the resistance of a liquid to flow.

It measures how thick or thin a liquid is.

Example:

Honey has high viscosity.

Water has low viscosity.

In pharmacy, viscosity is important in syrups, suspensions, and emulsions.

SECTION B – Long Answer Section

This section includes detailed questions related to solubility, surface tension, and ideal solutions. Students must explain concepts with diagrams, equations, and examples.

Question 1: Describe Solubility of Liquids in Liquids.

Answer:
Solubility of liquids refers to the ability of one liquid to dissolve in another.

Types of liquid mixtures:

Completely miscible liquids
Example: Alcohol + Water

Partially miscible liquids
Example: Phenol + Water

Immiscible liquids
Example: Oil + Water

Factors affecting solubility:

Temperature

Nature of solute and solvent

Pressure

In pharmaceuticals, solubility is important for drug formulation and drug delivery.

Question 2: Derive Raoult’s Law for Ideal Solutions.

Answer:
Raoult’s law states that the partial vapor pressure of a component in a solution is proportional to its mole fraction.

Formula:

PA=XA×PA0P_A = X_A \times P_A^0PA​=XA​×PA0​

Where:
P_A = vapor pressure of component A in solution
X_A = mole fraction of component A
P_A° = vapor pressure of pure component A

Applications in pharmacy include:

Determination of molecular weight

Understanding solution behavior.

Question 3: Explain Methods for Determination of Surface Tension.

Answer:

Surface tension can be determined by several methods:

Capillary Rise Method
Measures the height of liquid rise in a capillary tube.

Drop Weight Method
Measures the weight of drops formed from a liquid.

Du Noüy Ring Method
Uses a platinum ring to measure surface tension.

Surface tension plays an important role in emulsions, detergency, and drug absorption.

SECTION C – Descriptive Section

This section tests deeper knowledge of pharmaceutical physical chemistry such as isotonicity, buffers, complexation, and drug–protein interactions.

Question 1: Define Isotonicity and Explain Methods to Adjust It.

Answer:
Isotonic solutions have the same osmotic pressure as body fluids such as blood plasma.

Examples:
0.9% Sodium chloride solution.

Methods to adjust isotonicity:

Cryoscopic method

Sodium chloride equivalent method

White–Vincent method

These methods are used for ophthalmic and injectable preparations.

Question 2: Explain the Henderson–Hasselbalch Equation.

Answer:

The Henderson–Hasselbalch equation relates pH, pKa, and concentration of acid and salt in buffer solutions.

Formula:

pH=pKa+log⁡[Salt][Acid]pH = pKa + \log \frac{[Salt]}{[Acid]}pH=pKa+log[Acid][Salt]​

Applications:

Preparation of buffer solutions

Maintaining pH of pharmaceutical formulations

Stability of drugs.

Question 3: Explain Crystalline and Amorphous States.

Answer:

Crystalline State:

Molecules arranged in a regular pattern.

Sharp melting point.

Example: Sodium chloride.

Amorphous State:

Molecules arranged randomly.

No definite melting point.

Example: Glass.

Amorphous forms usually show higher solubility and faster drug dissolution than crystalline forms.